Relationships between soil organic matter and crop yield after biochar substrates application and their combination with mineral fertilizers on sandy soil

In this field study, under the soil conditions of southern Slovakia (Dolná Streda, sandy Haplic Arenosol), there were quantified the effects of biochar substrates (1. Effeco 50:50; 2. Effeco 33:33:33) in two rates (10 and 20 t.ha⁻¹) applied alone or in combination with mineral fertilization on soil organic matter (SOM) content and crop yields for period of 3 years (2018-2020) but also the linear relationships between SOM and crop yields depending on the application of biochar substrates and its combination with mineral fertilizers. The results showed that the content of soil organic carbon (SOC) increased from 8.5 g.kg⁻¹ in unfertilized control to 13.8 g.kg⁻¹ in Effeco 33:33:33 at 20 t ha⁻¹. However, SOC decreased from 13.6 g.kg⁻¹ in fertilized control to 10.1 g.kg-1 in Effeco 50:50 at 10 t.ha⁻¹. Biochar substrates and their combination with mineral fertilizers did not have a significant effect on changes in labile carbon in the soil. The effect on the crop yields was diametrically different in the first year after the application of biochar substrates compared to the second and third year. In the second and third year, the same trend was observed in the reaction to substrates – including a more robust effect on the increase in crop yields in the third year after the application of biochar substrates and also biochar substrates with mineral fertilizers. The linear relationships between SOC and crop yields were found only in biochar substrates alone treatments.